1. Field of the Invention
The invention relates generally to sealing devices for forming a fluid seal between rotating and stationary components of a machine and, more particularly, to a method of forming an abradable seal between the rotating and stationary components of turbomachinery equipment, e.g., a compressor.
2. Description of the Currently Available Technology
Energy savings and energy conservation are important considerations in the field of turbomachinery equipment. However, increased energy efficiency cannot be pursued without consideration of the costs involved in modifying the equipment to achieve such savings. If the cost of achieving an energy savings is greater than the benefit derived from the energy savings, the practical course of action would be to forego such a modification.
In the turbomachinery field, one way of accomplishing an increase in energy savings and an improvement in efficiency without a major increase in manufacturing costs is by reducing or eliminating gas leaks in the machinery, e.g., between the stationary and rotating components of the machinery. Excessive clearances between sealing devices located between the rotating and stationary components of turbomachinery equipment, such as compressors, have typically been a source of gas leaks, resulting in increased horsepower requirements and a loss of energy efficiency.
In order to reduce such gas leaks, sealing devices, such as metal or plastic sealing rings, labyrinth or knife edge seals, etc., are used. The most common seal design for centrifugal compressors is a labyrinth or knife edge seal. In this seal, a plurality of spaced apart labyrinth teeth on one component, e.g., the stationary component, are spaced from the other component by a small clearance. This simple seal works by contracting the gas as it flows through the close clearance points underneath the teeth and then expanding it between the teeth. This alternating contraction and expansion reduces the energy of the gas and lowers its flow rate. Leakage through the seal is proportional to the clearance. However, the clearance or gap between the sealing device and the rotating and/or stationary components must be controlled to a high tolerance. If the clearance is too small, the rotating component could rub the sealing device, possibly causing damage to both the rotating and stationary components. Also, sufficient clearance must be designed into the sealing device to allow for thermal expansion or surging of the machinery components during normal operation. Therefore, conventional metal or plastic sealing devices tend to be designed conservatively with respect to clearances, i.e., tend to have a relatively large sealing gap, e.g., 0.020xe2x80x3-0.030xe2x80x3, to help reduce the chance of component rubbing and machinery damage.
One way of improving the efficiency and energy savings of rotating turbomachinery is through the use of abradable seals, i.e., seals made of material that is low in resistance to abrasion. Such abradable seals permit smaller clearances than conventional metal or plastic machinery seals and reduce the risk of damage to the rotating and stationary components should a rub occur. For example, silicone rubber has been used as an abradable seal material in the gas turbine industry. However, these known silicone rubber seals typically must be vacuum molded in place. For this conventional vacuum molding procedure, a specifically dimensioned mold is required for each different seal size. Since a typical compressor may have between seven to fifteen different size seals, this requires seven to fifteen different size molds to form the different size seals. The cost of acquiring and maintaining these different size molds greatly increases the overall manufacturing costs of the turbomachinery equipment. Further, the time required to mold each individual seal increases production time. Additionally, if the machine is redesigned with a new, different size seal, a new mold also must be acquired for that new seal size.
Therefore, it would be advantageous to provide a method of forming a seal, particularly an abradable seal, for turbomachinery equipment which reduces or eliminates the problems associated with conventional seals and seal forming methods.
In the present invention, abradable sealing material is adhesively bonded to a machinery piece rather than being vacuum molded in place, as was done previously. In particular, the present invention provides a method of forming an abradable seal between rotating and non-rotating components of a machine. A sheet of abradable material having uniform thickness is formed and then cut to a desired shape to form an abradable sheet piece. An adhesive composition is applied to at least a portion of a substrate surface of one of the components and the sheet piece is contacted with the adhesive composition to adhesively bond the sheet piece to the component substrate.
An abradable seal is also provided comprising an adhesive composition deposited over at least a portion of a substrate surface with an abradable sheet piece bonded to the substrate by the adhesive composition.
A complete understanding of the invention will be obtained from the following description when taken in connection with the accompanying drawing figure.